What resolution did you played at? Play dolphin at your monitor native resolution, turn on pixel lighting, pixel depth, EFB to ram, go crazy with AA and AF. This should do the trick to bring up your gpu load.

Getting an accurate gpu load reading out of a program is flat out impossible unless it gives you the load of each piece of fixed function logic separately. Simply change settings like efb scale, SSAA, and pixel lighting until you start to see a drop, then you'll know that one of the pipeline stages has hit full load and you need to back off. With a GTX 570 3x efb scale + 4xSSAA should run smooth as silk in any games. But 9xSSAA and pixel lighting may be too much for some games.

@tuanming

By the way just so you know switching from efb to texture to efb to ram does not increase gpu load. It simply creates a memory bottleneck in exchange for accuracy (since you're copying the efb into and out of system ram instead of video ram, but it's still rendered the same way at the same resolution).

"Normally if given a choice between doing something and nothing, I’d choose to do nothing. But I would do something if it helps someone else do nothing. I’d work all night if it meant nothing got done."
-Ron Swanson

"I shall be a good politician, even if it kills me. Or if it kills anyone else for that matter. "
-Mark Antony

Currently, no single gpu is powerful enough to max out settings in pc games with a 2560x1600 a resolution to reach a stable 60+ fps. Dolphin on the other hand, put more tax or stress on the games' resolution than the typical pc res because it's doing more workloads than just merely playing games on pc. At least, this is how i think it goes.